1. Field of the Invention
The present invention generally relates to new ferrous complexes capable of being used as an electron transfer mediator in an enzyme-based biosensor, and more particularly, as an electron transfer mediator, the new ferrous complexes exchange an electron rapidly and smoothly between an enzyme and electrode, are strongly absorbed onto electrode and are stable, so that the new ferrous complexes allow excellent sensitivity of a biosensor to be maintained.
2. Description of the Related Art
In general, an electrochemical biosensor is a device for detecting various analysis objects in the environment, as well as in the fields of biology, medical science, and the like, and representatively, there is a biosensor for detecting analytes such as glucose, cholesterol, amino acids, and the like from human body fluids.
A glucose sensor is a type of biosensor, which is a device for measuring the concentration of glucose in blood or urine, and is used for diagnosing diabetes, or the like. Present commercially available electrochemical glucose sensors use mainly enzyme electrodes, and more specifically, have a structure whereby glucose oxidase is fixed on an electrode capable of converting electrical signals by using a chemical or physical method. As a basic principle, such an electrochemical glucose sensor measures the concentration of glucose in analytes by measuring current generated through transfer of electrons to the electrode, wherein the electrons are generated by oxidizing glucose in an analyte such as blood with enzymes.
In the case of a biosensor using an enzyme electrode, there is a problem that since the distance from an active center of the enzyme is too long, it is difficult to directly transfer electrons generated by an oxidization of the substrate to the electrode. Accordingly, an oxidation and reduction mediator, that is, an electron transfer mediator, is necessarily needed in order to easily perform such an electron transfer reaction.
Conventionally, examples of representative electron transfer mediators that are typically used include ferrocene, ferrocene derivatives, quinone derivatives, osmium derivatives, potassium ferricyanide, and the like. Among them, ferricyanide as a representative electron transfer mediator applied in commercially available biosensors is an anion that is bonded with six cyanide ligands around Fe3+ in an octahedral structure, and is easily oxidized with [Fe(CN6)]4−, in which its oxidation and reduction are reversible. Because of these properties, ferricyanide serves as a good representative electron transfer material in the electrochemical field, and is mainly used as an electron transfer mediator for biosensors. However, problems occur when ferricyanide is not strongly absorbed into the surface of electrode, and thereby is exposed to the solution, where it tends to be eliminated into the solution. Thus an amount of the electron transfer mediator available for a reaction with enzymes is reduced, thereby decreasing measurement sensitivity of blood glucose for a glucose sensor. For this reason, it is difficult to measure blood glucose accurately.